1. Field of the Invention
This invention relates to equipments having liquid drain lines which may undergo limited movement during use, and which must be connected to fixed drain conduits (e.g., commercial/industrial washing machines).
2. Description of Related Art
It is well known that small particles (i.e., particulates) can cause defects in integrated circuits formed upon semiconductor wafers. Such defects may prevent the integrated circuits from performing their intended functions. For example, a process called photolithography is used to pattern layers of desired materials deposited upon the semiconductor wafers. During photolithography, light passing through a pattern on a mask transfers the pattern to a layer of light-sensitive photoresist deposited over a layer of desired material. Particulates on the surface of the mask or on the surface of the photoresist layer which block or diffuse the light cause imperfect pattern registrations (i.e., imperfect feature formations). The resulting imperfect features formed within an integrated circuit may render the integrated circuit inoperable.
In order to help keep wafer processing areas as particle free, (i.e., "clean") as possible, such areas are designated as "clean rooms". Particulates may be present within the air in clean rooms, introduced by processing personnel, suspended in liquids and gasses used during wafer processing, and generated by processing equipment located within the clean rooms. As a result, the air within clean rooms is typically continuously filtered. Liquids and gasses entering clean rooms and used during processing are also filtered, and clean rooms typically exclude portions of processing equipment which generate particulates.
Air "cleanliness" levels of clean rooms are determined by the densities of different sizes of particulates present in the air and are specified using class numbers. The allowable densities of particulates within clean rooms is dependent upon the clean room class numbers and the largest dimensions of the particulates. For example, a class 1 clean room can have only 1 particle with a largest dimension of 0.5 micron in each cubic foot of air, but may have up to 34 particles with largest dimensions of 0.1 micron per cubic foot of air. The required class number for a particular clean room is largely determined by the feature sizes of the integrated circuit devices being produced within the clean room. Portions of many integrated circuits produced today are formed within class 1 clean rooms.
Humans continuously generate large numbers of particulates including dead skin cells and hairs. When working in clean rooms, personnel typically wear low-particle-generating coverings which almost completely envelope their bodies. The clean room garments essentially form filters around the wearers, reducing the number of particulates generated by the wearers which escape into the air. Exemplary garments include overalls and hoods, face masks, safety glasses or goggles, leggings, shoe covers, and gloves. Undergarments such as caps or nets may also be used to keep hair in place under hoods.
Clean room garments must be laundered on a regular basis if they are to remain functional and sanitary. The laundering process must, however, be carried out such that the clean room garments do not become sources of large number of particulates. For example, particles present in the water used to wash the clean room garments, or particles of a laundering agent (e.g., a detergent) added to the water, may become trapped in fibers of the clean room garments during laundering. Such particles may be released into the air during wear of the garments. Improper laundering may also damage the fibers of the clean room garments, causing them to break apart. In this case, small pieces of the fibers may be released into the air during wear. No matter how carefully the laundering process is carried out, transport of laundered clean room garments through the relatively "dirty" environment between an off-site laundering facility and the clean room presents a particle contamination problem. In fact, the plastic bags routinely used to protect laundered garments are themselves particle generators, rendering them ineffective in protecting clean room garments from the introduction of particles during transit. It is thus highly desirable to locate appliances used to launder clean room garments within the clean room itself.
Several different types of textile laundering appliances (e.g., commercial/industrial washing machines) use water to launder textiles (e.g., garments). One example of such a laundering appliance is a washer/extractor 10 depicted in FIG. 1. FIG. 2 is a side cross-sectional view of washer/extractor 10. Washer extractor 10 includes a cylindrical drum 12 mounted within a housing 14. During a typical use, soiled garments are placed within drum 12, drum 12 is filled to a certain level with water, detergent is added to the water in drum 12, and drum 12 is rotated about a horizontal axis 16 in order to flush foreign substances from the garments.
Drum 12 is essentially a hollow cylinder with circular plates covering both open ends of the hollow cylinder. In the embodiment of FIG. 2, drum 12 is divided into two compartments or "pockets" 18a and 18b of substantially equal volume by a planar partition 20. Partition 20 is perpendicular to and extends between both circular plates of drum 12. Three access doors 22 in the curved outer surface of drum 12 allow access to pocket 18a. Similarly, three access doors 24 in the curved outer surface of drum 12 allow access to pocket 18b. During use, pockets 18a and 18b are loaded with substantially equal weights of garments to minimize reciprocal motion imparted upon housing 14 by drum 12 due to the rotating eccentric masses of wet garments.
Washer/extractor 10 is designed for isolation of laundered and soiled garments, and subsequently has a load side 26 and an unload side 28. Soiled garments may be stored in an area adjacent to load side 26 and loaded into drum 12 from load side 26. Laundered garments are removed from drum 12 from unload side 28, and may be stored in an area adjacent to unload side 28. As a result, a significant amount of physical separation is achieved between laundered and soiled garments.
Washer/extractor 10 also includes an outer shell 30 surrounding drum 12 having two arcuate shell doors 32a and 32b. Shell door 32a is located on load side 26 of outer shell 30, and is shown in a closed position. When drum 12 is suitably rotated and shell door 32a is in an open position, shell door 32a allows access to access doors 22 for loading soiled garments into pocket 18a, and allows access to access doors 24 for loading soiled garments into pocket 18b. Shell door 32b is located on unload side 28 of outer shell 30, and is shown in an open position. As shown, shell door 32b allows access to access doors 22 for removing laundered garments from pocket 18a. When drum 12 is suitably rotated, open shell door 32b allows access to access doors 24 for removing laundered garments from pocket 18b.
Washer/extractor 10 includes a drain line 34 extending outwardly and downwardly from outer shell 30 for removing water from drum 12 by draining. A drain valve (not shown) between drum 12 and drain line 34 controls a flow of water from drum 12 into a top end of drain line 34. A floor 38 supports washer/extractor 10, and a bottom end of drain line 34 extends into an open trench 36 formed within floor 38. Trench 36 is connected to a sanitary sewer line 39 located directly below drain line 34.
In order to remove a substantial amount of water from the textiles within drum 12, the textiles may be subjected to "extraction" operations. During an extraction operation, drum 12 is rotated about horizontal axis 16 at a relatively high rate of speed. Centrifugal force acting radially upon the water retained by the textiles causes the water to leave the textiles and move from drum 12 to outer shell 30 through openings (e.g., perforations) in drum 12. During the relatively high rotational speeds employed during extraction operations, drum 12 may impart a substantial amount of reciprocal motion upon housing 14 and connected floor 38 due to the rotating eccentric masses of wet garments within drum 12. In order to mechanically isolate housing 14 and connected floor 38 from such reciprocal motion, drum 12 and surrounding outer shell 30 may be raised above a normal position and held there by a suspension system during extraction operations. FIG. 3 is a side cross-sectional view of washer/extractor 10 with drum 12 and surrounding outer shell 30 raised a height h above a normal position during such an extraction operation. Height h may be, for example, about 1.5 inches. The drain valve is typically open during extraction operations, allowing water to flow from drum 12 into drain line 34.
Drain line 34 is connected to outer shell 30, and thus moves with outer shell 30. In addition to the vertical movement of drain line 34 due to activation of the mechanical isolation system, drain line 34 may also undergo a significant amount of lateral movement during extraction operations due to the reciprocal motion of drum 12. As a result, a lateral clearance "c" about drain line 34 is typically incorporated into the dimension of the upper opening of trench 36 in order to accommodate the lateral movement of drain line 34 during extraction operations. Clearance c may be, for example, about 3.5 inches.+-.0.5 inch.
A problem arises when using washer/extractor 10 within a clean room environment. Due to clearance c about drain line 34 to accommodate the lateral movement of drain line 34 during extraction operations, a portion 40 of water 42 entering trench 36 from drain line 34 may splash out of the upper opening of trench 36 and onto floor 38 surrounding trench 36. Portion 40 of water 42 may contain dissolved chemicals (e.g., detergent) and/or particulate matter flushed from the textiles within drum 12. When the water evaporates, the previously dissolved particulates may become airborne. As such, portion 40 of water 42 represents a source of particulate contamination within the clean room.
It would thus be desirable to have a drain system which does not allow portion 40 of water 42 to splash out of the upper opening of trench 36 and onto floor 38 surrounding trench 36. When used with a laundering appliance installed within a clean room, such a drain system would reduce particulate contamination within the clean room.